In recent years, in connection with thermal power plants using a large amount of fossil fuel, study has been continued on a method of separating and recovering carbon dioxide contained in a combustion exhaust gas by allowing the combustion exhaust gas and an amine-based absorption liquid to come into contact with each other and a method of storing the recovered carbon dioxide instead of discharging the recovered carbon dioxide.
Specifically, there is known a carbon dioxide recovery system that includes an absorption tower and a regeneration tower. In the carbon dioxide recovery system, the absorption tower allows carbon dioxide contained in a combustion exhaust gas to be absorbed to an amine-based absorption liquid, and the regeneration tower is supplied with an absorption liquid (rich liquid) having carbon dioxide absorbed thereto, from the absorption tower, and recycles the absorption liquid by discharging a carbon dioxide gas from the rich liquid through the heating of the rich liquid. The carbon dioxide recovery system supplies the recycled absorption liquid (lean liquid) to the absorption tower to reuse the recycled absorption liquid (lean liquid).
In a step of discharging carbon dioxide from the rich liquid, a reboiler disposed near the regeneration tower circulates and heats the absorption liquid in the regeneration tower. A part of water vapor, which is generated to be used in a thermal power plant, a factory, or the like, is often supplied to the reboiler as a heating medium. In this case, the amount of heat, which is supplied to the absorption liquid of the regeneration tower from the heating medium of the reboiler, is determined from a difference between the amount of heat of water vapor at the inlet of the reboiler and the amount of heat of water at the outlet of the reboiler. The amount of heat of water vapor at the inlet of the reboiler is calculated from the product of the amount (enthalpy: kJ/kg) of heat retained per unit weight, which is determined through the measurement of temperature and pressure of water vapor, and the mass flow rate (kg/sec) of water vapor. Further, the amount of heat of water at the outlet of the reboiler is calculated from the product of the amount (enthalpy: kJ/kg) of heat retained per unit weight, which is determined through the measurement of temperature and pressure of water, and the mass flow rate (kg/sec) of water.
However, a part of the water vapor supplied to the reboiler does not condense (does not change into water), but remains in the form of water vapor. That is, a fluid existing at the outlet of the reboiler is a gas-liquid two-phase fluid where water vapor and water coexist. Moreover, a ratio between the flow rates of water vapor and water varies depending on the operating conditions of the carbon dioxide recovery system. A method of accurately measuring the ratio between the flow rates of water vapor and water has not been established.
For this reason, it was difficult to accurately measure the amount of heat, which is supplied to the absorption liquid of the regeneration tower from the heating medium of the reboiler, with the above-mentioned method in the related art that determines a difference between the amount of water vapor at the inlet of the reboiler and the amount of heat of water at the outlet of the reboiler.